The H-P-A axis is a key physiological system for detecting and responding to stress. While corticotropin releasing factor (CRF) regulates the response of this axis at the pituitary, hormones and neuropeptides derived from proopiomelanocortin (POMC) regulate the H-P-A axis at the adrenal cortex and in the central nervous system. Several lines of evidence suggest that adrenocortical responsiveness to ACTH is highly regulated and a component of H-P-A axis control. For example, the adrenal cortex demonstrates a circadian responsiveness to ACTH. POMC is produced not only in pituitary, but also in the hypothalamus and brainstem, and numerous effects of POMC peptides on control of neuroendocrine and other autonomic functions have also been reported. For example, evidence for short-loop feedback control of CRF production by centrally produced melanocortins has been described. Recently, this laboratory has cloned the adrenocortical receptor for ACTH and two neural receptors for the melanocortin peptides produced form POMC. These reagents are valuable tools for the analysis of H-P-A axis control both in the adrenal cortex and the central nervous system. The basic pharmacological properties of these receptors will be defined, and functional properties of these receptors will be examined in normal animals, in animals subjected to acute and chronic stress, and in transgenic mouse mouse models which perturb the H-P-A axis. After pharmacological characterization of the cloned ACTH receptor, the regulation of this receptor will be examined both in cell culture and animal models. ACTH binding experiments have suggested that this receptor will be examined both in cell culture and animal models. ACTH binding experiments have suggested that this receptor is actually upregulated by its ligand, ACTH, and as such this receptor displays an unusual type of receptor regulation. The experiments proposed should provide mechanistic explanations for this unique mode of receptor regulation. The role of the ACTH receptor in a human disease, familial ACTH resistance, will be also be examined, and may provide information regarding the etiology of this disease, which is suggested to result from an ACTH receptor defect. The two neural melanocortin receptors, MC3-R and MC4-R, will be characterized pharmacologically, and using histochemical methods to determine their neuroanatomical distribution in the brain. These receptors will also be deleted from the mouse genome using homologous recombination in ES cell in order to define their role in H-P-A axis control. These experiments should contribute to our understanding of the role of the adrenal cortex and central nervous system in H-P-A axis.